Gaspare Aselli (or Asellio) (c. 1581 – 9 September 1625)[1] was an Italian physician noted for the discovery of the lacteal vessels of the lymphatic system.

Aselli is regarded as the discoverer of the lacteals, or the set of vessels which absorb or suck up the nutritious portion of the food of animals, i.e., the chyle from the upper part of the intestinal tube, in order to convey it to the heart and lungs, so that it may become incorporated in the circulating fluid or blood.

He traced them to a group mesenteric glands still known as “Aselli's gland” or “pancreas Aselli”, and believed that they passed on into the liver, thus failing to trace their true ending; it was not until Jean Pecquet's discovery of the thoracic duct and its continuity with the lacteal vessels that the process of absorption was clearly established.

[6] By highlighting the existence of chyliferous vessels and lymphatic circulation, Aselli’s discovery greatly contributed to debunking Galen's generally accepted theory that the liver was the source of the blood – a belief that was definitely disproved by William Harvey in his seminal work De Motu Cordis.

Shortly before De motu cordis (1628) appeared, Aselli anticipated William Harvey's monumental discovery of the circulation of the blood.

[10][11] The experimentation on living animals, and particularly the vivisection used by Gaspare Aselli provided the basis for much of the subsequent investigation of the human physiology.